1. Field of the Invention
The invention generally relates to magnetic recording systems and, in particular, to flexible suspension systems for magnetic recording heads.
2. Description of Related Art
A rigid disk drive or "hard disk" conventionally includes a magnetic recording head to encode date on a spinning recording disk. The magnetic recording head commonly consists of a magnetic transducer and a slider or hydrodynamic air bearing. The slider, having very flat, highly polished surfaces, "flies" above the spinning disk by floating on a boundary layer of air carried along the surface of the rotating disk.
In the assembled disk drive, a suspension suspends the magnetic head over the disk in a cantilever fashion. The suspension commonly includes a flexure which attaches the magnetic head to a free end of a suspension load beam. The load beam, in turn, is secured at a fixed end to an actuator suspension arm which moves the load beam and, thus, the magnetic head across the magnetic disk in operation.
Conventional rigid disk drives include a series of stacked disks positioned directly above one another. In order to decrease the size of the disk drive, the spacing between the disks becomes very important. Thus, disk drive manufacturers have become cognizant of the overall thickness of the suspension-magnetic head assembly (i.e., the dimension of the assembly measured in a direction perpendicular to the disk).
For accurate and dense data encoding, a read/write gap of the transducer must be maintained as close to the disk as possible at a constant height, typically about 6 micro-inches above the disk. The storage capacity of the disk is extremely dependent upon the height at which the read/write gap flies above the disk (i.e., the flying height). With an increase in the flying height of the read/write gap above the disk, the disk area encoded or read by the read/write gap increases. Hence, it is very important to keep the flying height as small as possible without having the magnetic head contact the disk in order to maximize the storage capacity of the recording disk; thus, it is preferred that the magnetic head fly at a constant height.
Magnetic disks, however, typically include undulations over the disk surface. To maintain a constant flying height, the magnetic head must follow the topography of the disk surface. Thus, the suspension must allow the magnetic head to roll around an x-axis (which aligns with the longitudinal axis of the load beam) and to pitch around a y-axis (which is orthogonal to the x-axis in the plane of the load beam). If the magnetic head does not follow the out of plane motion of the disk, the magnetic head will fly at a height greater than the desired flying height.
Additionally, the suspension should be extremely rigid in the x-y plane (i.e., in a plane parallel to the disk), to accurately place the magnetic head over the data track. That is, the suspension must not permit the load beam to move from side to side (i.e., yaw) in the x-y plane about its fixed end. Yawing of the magnetic head about the fixed end of the suspension moves the transducer across data tracks, causing the transducer to encode data outside of the desired track (i.e., causing "off track error").
Torsional resonance of the suspension also moves the magnetic head across data tracks. Torsional resonance typically occurs during data seek operations in which the actuator moves the suspension over the disk; other sources, including external disturbances, can also cause the suspension to resonate. The cross track movement of the magnetic head results because the amplitude of the resonance increases away from the longitudinal axis of the load beam, and thus, the greater the dimension between the magnetic head and the longitudinal axis of the load beam, the greater the displacement of the magnetic head across the disk surface due to torsional resonance of the load beam.
In the standard 3370-type suspension, as disclosed in U.S. Pat. No. 4,167,765 to Watrous, the flexure distances the magnetic head from the plane of the load beam. Thus, the geometry of prior suspension amplifies the magnitude of magnetic head displacement due to torsional resonances, leading to error in the positioning of the magnetic head.
This behavior not only reduces the track density, because wider tracks are necessary to compensate for the resulting movement of the magnetic head over the disk surface, but also interferes with the electronic data-track following capability of a control feedback system. During suspension resonance, extreme cross-track modulation of the transducer confuses the track following electronics and causes mechanical instability in the system. Potentially, actuator instability can lead to violent oscillations of the transducer suspension, causing the head to contact the disk and possibly destroy data.
A prior patent to Watrous, U.S. Pat. No. 3,931,641, discloses a suspension less susceptible to the effects of torsional resonance. The disclosed suspension includes a central finger with a cantilevered end which supports the magnetic head. Although the suspension allows the magnetic head to follow the disk topography, it is susceptible to slip-stick phenomenon. That is, during torsional resonance, the magnetic head yaws across the disk surface, deflecting the central finger in a plane parallel to the x-y plane. Due to frictional forces between the central finger and a load point of the suspension, the finger sticks in a position off of the undeflected longitudinal axis of the central finger (i.e., sticks in an "off-axis position"). The deflected central finger eventually springs back and causes cross track error.
U.S. Pat. No. 4,868,694 to Hagen discloses a flexure having greater radial stiffness to prevent the magnetic head from deflecting and sticking in an off-axis position. The disclosed suspension, however, does not provide enough flexibility to permit the head to follow out of plane motion of disk to minimize variations in flying height.
The standard 3370-type suspension additionally poses assembly problems. The flexure of the 3370-type suspension, as disclosed in the '765 patent, includes a protuberance or dimple which contacts and pivots about a load support point. In assembly, the magnetic head is preferably positioned to vertically align the center of gravity of the magnetic head with the dimple of the flexure. Precision positioning between the magnetic head and flexure, however, is difficult; the tolerances of the components and the tolerances of the tooling used to center the components stack up and make its very difficult to precisely control the position of the magnetic head relative to the dimple. Thus, although it is desired that the magnetic head center of gravity vertically aligns with the flexure dimple, assembled magnetic head/flexure assemblies seldom meet this requirement.
Prior suspension designs address one or more of the aforementioned design criteria. No single suspension design, however, adequately addresses and resolves all of the foregoing problems. Thus, a there is a need for a suspension which limits the effect of suspension torsional resonance on the magnetic head while providing sufficient flexibility to allow the magnetic head to follow the topography of the recording disk. In addition, there is a need for a suspension/magnetic head assembly which is readily assembled with the flexure to vertically align the center of gravity of the magnetic head with a protuberance.